The design of systems to control spas is complicated by the environment of the spa. Typically, spa control systems contain heating elements, controls, switches, and wiring harnesses which deteriorate when exposed to moisture or extreme levels of humidity and a hostile chemical environment. Since the chemically treated, heated water of the spa raises the humidity level and produces corrosive gases, the atmosphere surrounding the controls of the spa unit is inherently corrosive to spa control systems.
The accuracy of the temperature of the spa water is essential to the safety and comfort of the spa user. This temperature is difficult to accurately control, since the temperature of the water can vary rapidly depending on the number of spa users, the ambient temperature of the air, and other environmental factors. To conserve energy, the spa temperature is customarily raised to the desired level shortly before the expected use of the spa, and is not maintained at a constant temperature when the spa is unattended. Depending on the use of the spa, the temperature of the spa water may be cycled several times per day. During these cycles, the control of the water temperature is difficult to maintain without overheating or underheating the water. Typically, a spa control system merely heats the water with a heating element until the temperature of the water matches a predetermined setting selected by the spa user. Since the heating element is not turned off until that desired water temperature is reached, the residual heat in the heating element may increase the temperature of the water beyond the actual temperature desired. Conversely, the location of the temperature sensor may be located in the spa in such a fashion that it does not sense the actual, median water temperature. Accordingly, the heating element may be turned off before the temperature of the water reaches the desired level.
Present spa controllers operate on line voltages which can present a safety hazard to the spa users. To meet desired safety specifications, these controls are typically located away from the sap, however, this separation is inconvenient to the spa user.